<!DOCTYPE html>
<html lang="en" xmlns:v-bind="http://www.w3.org/1999/xhtml">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<!--view层 模板-->
<div id="app">

    下拉框:
    <select v-model="selected">
        <option value="" disabled>--请选择--</option>
        <option>A</option>
        <option>B</option>
        <option>C</option>
    </select>

    <span>选中了:{{selected}}</span>
</div>

<!--第一步，导入Vue.js-->
<script src="https://cdn.jsdelivr.net/npm/vue@2.5.21/dist/vue.min.js"></script>

<script>
    var vm = new Vue({
        el:"#app",
        //Model:数据
        data:{
           selected: ''
        }
    });
</script>
</body>
</html>